Presently, there is much effort being devoted towards the development of a personal data card which is a credit-card-sized device containing an electronic memory for storing data in electronic form. An example of such a personal data card is described in U.S. Pat. No. 4,921,160, issued on May 1, 1990, in the names of Richard Flynn and Fred Verdi, and assigned to AT&T. In the past, personal data cards have been fabricated from a conventional circuit board, made from FR-4 or a polyester resin, which has a layer of metallization of copper or the like clad to one or both of its major surfaces. The copper metallization is patterned, typically by photolithographic techniques, to yield a circuit comprised of a plurality of metallized pads and conductive paths selectively interconnecting the pads. In practice, the metallized pads are selectively plated first with nickel and then gold to facilitate wire bonding of each of a plurality of aluminum leads of a semiconductor die to the circuit board.
While the use of FR-4 or polyester resin-based circuit boards in the fabrication of personal data cards is widespread, the cost of such circuit boards often represents a sizable fraction of the overall cost of the card itself. For this reason, efforts have been focused on employing a less expensive interconnection media in the fabrication of a personal data card. One type of interconnection media which offers a cost advantage over conventional FR-4 and polyester resin-based circuit boards is a polymer thick-film circuit. Such circuits are typically comprised of a sheet of polymer (e.g., MYLAR.RTM. film) having a conductive ink printed thereon to yield a pattern of conductive pads and interconnecting paths. Connection of a component to a set of the electrically conductive ink pads on the polymer thick-film circuit is accomplished either by soldering or by use of a conductive adhesive.
While polymer thick-film circuits are less expensive to fabricate than conventional FR-4 and polyester resin-based circuit boards, such thick-film circuits have not replaced conventional circuit boards in the fabrication of personal data cards. One reason why is that, heretofore, it has not been possible to make a reliable wire bond between each aluminum lead, associated with a semiconductor die, and an ink pad on a polymer thick-film circuit. Wire bonding is the preferred technique for reliably achieving an electrical connection between each semiconductor die and the interconnection media in fabricating a personal data card because of the fine pitch of the aluminum leads associated with the die.
Further, with present-day polymer thick-film circuits, the conductive pads and interconnecting paths, created by depositing conductive ink onto the polymer film, have an impedance which is thought to be suitable only for dc circuits found in contact-type personal data cards. As their name implies, contact-type cards have a set of electrical contacts designed for physical mating with a corresponding set of contacts on a corresponding card reader, thus allowing dc to be coupled t the card directly to power the active components on the card. On the other hand, the impedance of the conductive ink paths and interconnecting pads on current-day polymer thick-film circuits is generally regarded as being too high for ac circuits found in contactless personal data cards. Contactless personal data cards are characterized by an absence of any contacts for physically making connection to a card reader. Instead, present-day contactless cards generally are provided with inductive and/or capacitive coupling means for coupling signals and power to the card. As may be appreciated, with contactless-type personal data cards, the dc needed to power active components on the card must be generated on the card itself from the ac coupled thereto. Hence, contactless cards carry one or more ac circuits not found on contact-type cards.